The project will build on previous work at the University of Strathclyde to model the development of microstructure in renewable and compostable semi-crystalline plastic films. The plastic’s microstructure, that is how its crystalline domains are spatially arranged to leave amorphous polymer pathways throughout the material, dominates its material properties. These include its strength, flexibility, and optical transparency, as well as the essential gas barrier properties required, for example, in food packaging applications. Understanding how the microstructure evolves in plastics, and how it is influenced by processing conditions and additives such as filler particles, is essential to its control and therefore for the design of manufacturing routes to optimise application-specific properties.

To improve the properties of plastic films, and to make them processable, a blend of plasticisers and fillers are usually added to the polymer melt. This means that there are many competing interactions to understand across a range of length and timescales. In this project, we will explore how to make the filler particles act as nucleants for the polymer crystals, using both coarse-grained and atomistic models. The work will focus on polyhydroxybutyrate (PHB), a renewable and compostable polymer created by bacteria and a potential competitor for traditional oil-based plastic films used in food applications [1].

The crucial step-change we propose for this project is to employ meso-scale microstructure models to design optimum interfacial properties for the filler particles. The optimum microstructure will require a bespoke density of nucleation sites on the filler particles, in order to create microstructures that promote mechanical flexibility while inhibiting gas diffusion through the amorphous pathways that percolate through the material. Coarsegrained [2] and atomistic models [3] will then be used to investigate the impact surface functionalisation has on nucleation and crystalline structure at the interface with the filler, allowing optimum filler-particle coatings to be selected for the proposed material design.

[1] M Majerczak, D Wadkin-Snaith, V Magueijo, PA Mulheran, J Liggat, K Johnston, Polyhydroxybutyrate: a review of experimental and simulation studies of the effect of fillers on crystallinity and mechanical properties, Polymer International, 71;1398 (2022).

[2] D Wadkin-Snaith, PA Mulheran, K Johnston, The impact of plasticisers on crystal nucleation, growth and melting in linear polymers, Polymer 340;127095 (2024).

[3] N. Middleton, PA Mulheran, K Johnston, Atomistic modelling of PHB, in prep.

Further information

Postgraduate Certificate in Researcher Development

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